1. Field of the Invention
The present invention relates to a fixing unit including a removal unit that removes unfixed developer adhered to a fixing roller or a pressure roller, and to an image forming apparatus including such a fixing unit.
2. Description of the Related Art
An image forming apparatus based on electrophotography forms a desired toner image on a photoconductive drum, and after transferring the toner image on the photoconductive drum to a paper, fixes the toner image onto the paper by a fixing unit. The fixing unit usually includes a pair of heaters. A typical example of the pair of heaters is a fixing roller and a pressure roller disposed so as to be pressed against each other with a paper feeding path held therebetween. This type of fixing unit holds the paper between the fixing roller and the pressure roller, and applies heat and pressure to the paper to thermocompressively fix the toner image onto the paper, thus completing image forming on the paper.
In such a fixing unit, since at least either of the fixing roller or the pressure roller contacts the toner applied to the paper, the toner may adhere to the fixing roller or the pressure roller during the fixing process. Besides, the toner that has adhered to either of the fixing roller or the pressure roller often adheres to the other, via the contact interface therebetween.
To avoid this, for example Japanese Patent Application Laid-Open No. 05-119661 proposes a fixing unit provided with a brush type cleaner disposed so as to contact the fixing roller, to thereby remove the toner adhere thereto.
FIG. 1 is a schematic cross-sectional view showing an internal structure of a conventional fixing unit provided with a cleaner. The fixing unit shown in FIG. 1 includes a fixing roller 201 and a pressure roller 202 inside a housing 200 which constitutes a frame of the apparatus. The fixing roller 201 is a hollow cylindrical-shaped roller including a heater lamp 201a therein, which maintains a predetermined temperature of the roller surface. The pressure roller 202 is a cylindrical-shaped roller pressed against the fixing roller 201, so as to provide a fixing nip of a predetermined width with the fixing roller 201. When a paper P to which a toner T has adhered is conveyed to the fixing unit, the fixing roller 201 and the pressure roller 202 applies heat and pressure to the paper P while feeding the paper P held therebetween, to thereby fix the toner image on the paper.
On the circumferential surface of the pressure roller 202, an oil supplier 203, a cleaning roller 204 and a separating blade 205 are disposed. The oil supplier 203 applies an oil to the surface of the pressure roller 202 via an oil applicator 203a, for smooth separation of the paper P from the pressure roller 202. The cleaning roller 204 includes a core metal 204a and a brush portion 204b radially implanted on the core metal 204a, to serve to remove the unfixed toner stuck to the pressure roller 202. The separating blade 205 is pressed against the circumferential surface of the pressure roller 202, to peel off from the pressure roller 202 the paper P on which the toner has been fixed. The paper P separated from the pressure roller 202 passes through a paper guide 206 and is discharged outward by a discharge roller 207.
The conventional fixing unit thus constructed utilizes the brush portion 204b of the cleaning roller 204 to remove the toner stuck to the pressure roller 202 after the fixing process. However, since a portion of the toner adheres to the brush portion 204b, the toner adheres again to the pressure roller via the mutual contact point, when the cleaning roller 204 has made one rotation.
Besides, the brush 204b is generally made of a flexible synthetic resin. Accordingly, when the brush portion 204b removes the unfixed toner, a portion of the toner may be flipped by the tip of the brush portion 204b, thus to splash inside the housing 200. The toner that has splashed not only contaminates the interior section of the housing 200, but also often adheres to the pressure roller 202 and the paper P being conveyed, which leads to degradation in the printed image quality.